package com.epro.dx.widget;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.Scroller;

/**
 * 仿Launcher中的WorkSapce，可以左右滑动切换屏幕的类
 * @author Yao.GUET
 * blog: http://blog.csdn.NET/Yao_GUET
 * date: 2011-05-04
 */
public class FlingGallery extends ViewGroup
{
    //    private static final String TAG = "ScrollLayout";
    
    private Scroller mScroller;
    
    private VelocityTracker mVelocityTracker;
    
    private int mCurScreen;
    
    private int mDefaultScreen = 0;
    
    private static final int TOUCH_STATE_REST = 0;
    
    private static final int TOUCH_STATE_SCROLLING = 1;
    
    private static final int SNAP_VELOCITY = 600;
    
    private int mTouchState = TOUCH_STATE_REST;
    
    private int mTouchSlop;
    
    private float mLastMotionX;
    
    //    private float mLastMotionY;
    
    public FlingGallery(Context context, AttributeSet attrs)
    {
        this(context, attrs, 0);
    }
    
    public FlingGallery(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
        mScroller = new Scroller(context);
        
        mCurScreen = mDefaultScreen;
        mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    }
    
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b)
    {
        
        int childLeft = 0;
        final int childCount = getChildCount();
        
        for (int i = 0; i < childCount; i++)
        {
            final View childView = getChildAt(i);
            if (childView.getVisibility() != View.GONE)
            {
                final int childWidth = childView.getMeasuredWidth();
                childView.layout(childLeft, 0, childLeft + childWidth, childView.getMeasuredHeight());
                childLeft += childWidth;
                
            }
        }
        
    }
    
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        
        final int width = MeasureSpec.getSize(widthMeasureSpec);
        //        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        //        if (widthMode != MeasureSpec.EXACTLY)
        //        {
        //            throw new IllegalStateException(
        //                    "ScrollLayout only canmCurScreen run at EXACTLY mode!");
        //        }
        //        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        //        if (heightMode != MeasureSpec.EXACTLY)
        //        {
        //            throw new IllegalStateException(
        //                    "ScrollLayout only can run at EXACTLY mode!");
        //        }
        // The children are given the same width and height as the scrollLayout
        final int count = getChildCount();
        for (int i = 0; i < count; i++)
        {
            getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
        }
        // Log.e(TAG, "moving to screen "+mCurScreen);
        scrollTo(mCurScreen * width, 0);
    }
    
    /**
     * According to the position of current layout
     * scroll to the destination page.
     */
    public void snapToDestination()
    {
        final int screenWidth = getWidth();
        final int destScreen = (getScrollX() + screenWidth / 2) / screenWidth;
        snapToScreen(destScreen);
    }
    
    public void snapToScreen(int whichScreen)
    {
        // get the valid layout page
        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
        if (getScrollX() != (whichScreen * getWidth()))
        {
            
            final int delta = whichScreen * getWidth() - getScrollX();
            mScroller.startScroll(getScrollX(), 0, delta, 0, Math.abs(delta) * 2);
            mCurScreen = whichScreen;
            invalidate(); // Redraw the layout
        }
    }
    
    public void setToScreen(int whichScreen)
    {
        whichScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
        mCurScreen = whichScreen;
        scrollTo(whichScreen * getWidth(), 0);
    }
    
    public int getCurScreen()
    {
        return mCurScreen;
    }
    
    @Override
    public void computeScroll()
    {
        if (mScroller.computeScrollOffset())
        {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        
        if (mVelocityTracker == null)
        {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
        
        final int action = event.getAction();
        final float x = event.getX();
        //        final float y = event.getY();
        
        switch (action)
        {
            case MotionEvent.ACTION_DOWN:
                if (!mScroller.isFinished())
                {
                    mScroller.abortAnimation();
                }
                mLastMotionX = x;
                break;
            
            case MotionEvent.ACTION_MOVE:
                int deltaX = (int)(mLastMotionX - x);
                mLastMotionX = x;
                
                scrollBy(deltaX, 0);
                break;
            
            case MotionEvent.ACTION_UP:
                // if (mTouchState == TOUCH_STATE_SCROLLING) {
                final VelocityTracker velocityTracker = mVelocityTracker;
                velocityTracker.computeCurrentVelocity(1000);
                int velocityX = (int)velocityTracker.getXVelocity();
                
                if (velocityX > SNAP_VELOCITY && mCurScreen > 0)
                {
                    // Fling enough to move left
                    snapToScreen(mCurScreen - 1);
                }
                else if (velocityX < -SNAP_VELOCITY && mCurScreen < getChildCount() - 1)
                {
                    // Fling enough to move right
                    snapToScreen(mCurScreen + 1);
                }
                else
                {
                    snapToDestination();
                }
                if (mVelocityTracker != null)
                {
                    mVelocityTracker.recycle();
                    mVelocityTracker = null;
                }
                // }
                mTouchState = TOUCH_STATE_REST;
                break;
            case MotionEvent.ACTION_CANCEL:
                mTouchState = TOUCH_STATE_REST;
                break;
        }
        
        return true;
    }
    
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev)
    {
        
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) && (mTouchState != TOUCH_STATE_REST))
        {
            return true;
        }
        
        final float x = ev.getX();
        //        final float y = ev.getY();
        
        switch (action)
        {
            case MotionEvent.ACTION_MOVE:
                final int xDiff = (int)Math.abs(mLastMotionX - x);
                if (xDiff > mTouchSlop)
                {
                    mTouchState = TOUCH_STATE_SCROLLING;
                    
                }
                break;
            
            case MotionEvent.ACTION_DOWN:
                mLastMotionX = x;
                //                mLastMotionY = y;
                mTouchState = mScroller.isFinished() ? TOUCH_STATE_REST : TOUCH_STATE_SCROLLING;
                break;
            
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                mTouchState = TOUCH_STATE_REST;
                break;
        }
        
        return mTouchState != TOUCH_STATE_REST;
    }
    
}